This lens does not have the largest aperture out there, being limited to f/5 at the 200mm end and f/6.3 at the 500mm end. However, the advantage is that the lens is much smaller and lighter than the Nikon and Canon equivalents which do have larger apertures.

For the price, it's a hard lens to beat; the manual focus is nice and smooth, and the images are sharp even wide open. It's not going to match up to a 400mm Canon L, but it also costs 1/5th as much, and weighs a lot less, so that's the tradeoff.

My interest in the lens resulted froman interest in a long lens I could carry along with my 4x5 kit, and a big, heavy 400mm f/4 lens would, even if I could budget it, not fit that bill, as my 4x5 kit already weighs nearly 40 pounds.

Since my Nikon body is a manual focus body, I have not tried the autofocus, so I cannot comment on its performance. I can only say that I have gotten good results using this lens to photograph birds, and that it is best used on a tripod, especially at the long end.

With those caveats in mind, I would recommend this lens to anyone looking for a lightweight supertele lens on a budget.